The invention pertains to a crucible for the induction melting or super heating of metals, alloys, or other electrically conductive materials with at least three palisades, which are set up vertically and parallel to each other a certain distance apart and distributed around an arc of a circle in such a way as to surround the melt; with a part in the form of a circular plate, which forms the bottom of the crucible and supports the palisades, the palisades being provided at least in part with cavities, through which a coolant flows; and with an induction coil, which is wound around the outside of the palisades a certain distance away and which carries an alternating current.
A process for the melting of difficult-to-melt metals, especially tantalum, tungsten, thorium, and alloys of these metals in a water-cooled container is known (DE 518 499), the container consisting in this case of materials such as quartz glass, copper, or silver, which melt at temperatures that are lower than the melting point of the material to be melted. The means used to supply the energy required for melting and the means used to cool the container are devised in such a way that the material to be melted is melted completely without being contaminated by the crucible material. The crucible itself can be heated by means of an induction coil. The crucible is built up of individual segments, which are separated from each other by an insulating layer of, for example, mica, to prevent the current in the crucible from circling all the way around.
U.S. Pat. No. 3,461,215 discloses a induction crucible which is assembled from a plurality of palisades, all of which are arranged vertically and parallel to each other on a circular bottom plate to form a hollow cylinder. Cooling water flows through all of the electrically and thermally conductive palisades, which are also surrounded by an induction coil. The bottom plate of ceramic material is provided with a plug, through which the melt can be withdrawn. Strips of insulating material are inserted between the palisades.
U.S. Pat. No. 4,738,713 discloses a crucible for the slagless melting of high-purity reactive metals in a vacuum chamber, in which cooling water flows through the palisades, which are surrounded by the induction coil and which are screwed tightly to a circular bottom plate. The tubular palisades are separated from each other by slots, but all of them are in electrical contact with each other by way of the bottom plate, which is made of metal.
The known crucibles Suffer from the disadvantage of comparatively poor thermal efficiency. Thus the attempt was made to reduce the amount of heat lost by the Cooled palisades by adding insulating material to the melt, but this led in turn to a certain, although only slight, contamination of the melt (Schippereit et al.). Even this slight contamination of the melt material, however, is undesirable in many modern applications, and therefore this process has been accepted by industry to only a limited extent.
The arrangement and design of the palisades themselves and their electrical connection to each other or their insulation from each other have already been the object of numerous investigations. U.S. Pat. No. 3,223,519, for example, describes crucible segments which are insulated from each other, whereas in the case of the crucible according to U.S. Pat. No. 4,738,713, the palisades are set up a certain distance apart and connected to each other electrically.